Perpendicular magnetic recording (PMR) has been the prevailing writer technology for state-of-the-art magnetic hard disk drives (HDD). The magnetic pole in a PMR write head has a stringent geometric requirement. The pole thickness cannot be either too thin, a condition that causes pole erasure at remanence, or too thick which results in excessive magnetic flux that induces unwanted erasure at adjacent or far track locations. Furthermore, pole thickness at the air bearing surface (ABS) must be above a certain minimum value to avoid degrading performance in high data rate (HDR) application drives. Pole thickness at the ABS must not be too thick in order to prevent skew angle performance loss due to the different zones in the drive that are known as the inner region (ID), middle region (MD), and outer region (OD). The pole's ABS geometry also needs a bevel angle for the same purpose of guaranteeing its functionality at various skew angles encountered when the head operates at different radii (i.e. inner, mid, or outer) on the disk. These complex geometric shapes have to be fabricated with a high Bs and yet soft magnetic material in order to erase existing data patterns written previously, and replace them with sharp transitions from the new data.
There are generally two ways to fabricate the main pole that are called subtractive and additive methods. In the additive process, the desired geometric shape is created through photolithography followed by reactive ion etching (RIE) or ion beam etching (IBE) to form an opening in an insulation layer. Then, a magnetic material is deposited to fill the opening by either a plating process or a typical dry film deposition process such as ion beam deposition or sputtering. The subtractive process involves first depositing a magnetic film to cover a large area. Subsequently, photolithography and IBE are used to shape the magnetic material into a main pole structure.
With regard to the additive method, plating into a small cavity is a delicate process. Since the magnetic material usually grows from all sides of the cavity wall and meets at the middle of the opening, it is quite common to produce some voids or seam lines where the magnetic material converges at the center of the opening. The resulting void or seam line typically has significant porosity and yields a density and a saturation magnetic moment less than the surrounding bulk material. A similar situation occurs when dry film deposition is used to fill small cavities. In addition, the dry film deposition leaves a substantial residual stress in the film that may degrade the performance of the magnetic layer as observed by higher coercivity and/or lower permeability.
Annealing is usually employed to improve magnetic performance in films with residual stress. For example, C. Bonhote, E. Cooper, L. Romankiw, and H. Xu describe an annealing method in “Electroplated 2.4 Tesla CoFe Films”, K2-Seventh International Symposium on Magnetic Materials, Processes and Devices, Oct. 20-25, 2002. In some cases, very high temperature annealing is able to dramatically improve the permeability of magnetic material, particularly for higher frequency applications. However, high temperature annealing is usually not compatible with advanced PMR head designs, especially since the adjacent read head sensor is temperature sensitive. As PMR technology is pushed to higher areal density, the track pitch becomes progressively smaller. A size of less than 50 nm is required in the near future for next generation products. In the additive approach, a void or seam line represents a relatively large feature for small main pole volumes, and especially when the defect is located in the narrow write pole portion adjacent to the ABS.
Thus, there is an urgent need to develop a methodology that can enhance the magnetic integrity of a main pole structure in designs with small track pitch sizes. The new concept for improving write head performance must address the issue of small voids and seam lines in magnetic layers without degrading other components in the PMR write head or in the adjoining read head.